A number of purposes can be served by flushing the urinary bladder such as post-surgical treatment following surgery inside the bladder, i.e., at the prostate. As a rule, the instrument placed in the bladder is a flexible catheter, typically a balloon catheter device which admits a constantly flowing flushing liquid into the bladder and then drains it.
Flushing also is used during cutting surgical intervention inside the bladder, for instance at the bladder wall. The instrument introduced into the bladder then is a rigid endoscope with optics and a cutting device, typically a high-frequency driven loop. In this case, flushing serves to create a clear field of view by washing away blood and cut-off tissue pieces from the field of view.
The flushing of the urinary bladder can be carried out using a variety of instruments such as a two-duct catheter or a two-duct endoscope. However, intervention using two instruments placed separately into the bladder also is possible, one typically being inserted through the urethra and the other being put in place by means of a suprapubic trocar directly through the skin into the bladder. In the latter case one of the two ducts required for flushing may be present in one of the instruments and the other in the second instrument. Alternatively, both ducts may be present in one instrument put in place supra-pubically.
Care always must be taken during flushing that the bladder is filled in the same manner as much as possible. If the pressure inside the bladder is too low, it will collapse. This can be dangerous, especially during surgery inside the bladder, because then the rear bladder wall suddenly drops onto the instrument and can be injured.
On the other hand, excessive bladder pressure is undesirable. During flushing there are always fresh cut wounds in the bladder through which the patient's blood circulation is open to the bladder. If the bladder pressure is excessive, the flushing liquid can enter the patient's blood stream which can lead to the so-called TUR syndrome (transurethral resection syndrome). The TUR syndrome is dangerous and must be avoided under any circumstance. When surgery is being performed on a tumor, excessive pressure also creates the dangerous possibility of washing tumor cells into the patient's bloodstream.
Excessive bladder pressure is also a drawback in post-surgery flushing. Scars over freshly operated bladder sites may tear open because of excessive pressure, thereby delaying wound healing.
Besides methods of continuous flushing in which a supply line continuously feeds liquid and a drain line continuously evacuates it, there are also intermittent flushing methods requiring only one duct alternatingly serving as feed and as drain duct. Again, care must be taken to see that, when the liquid is introduced, the maximum bladder pressure is not exceeded, and then that the bladder is emptied in due time and filled again.
The desired bladder pressure is in the order of a few tens of centimeters of water head. Typically, the pressure is controlled by valves in the feed or the drainage. The surgeon optically watches the bladder filling, that is, he views the inside of the bladder through the endoscope optics. Manually actuated valves allow him to control the bladder pressure.
Although exceedingly costly, electronically controlled pumps are known to regulate the bladder pressure in devices of the above mentioned type and such pumps assure equality of feed and drain flows at all times. While the bladder volume is thereby kept constant, the pressure is not. Externally created effects tending to raise the pressure, i.e., from causes outside of the flushing system such as external pressure on the bladder or respiratory pressure changes, lead to increases in pressure that this control means cannot handle.
German patent document 35 40 326 C2 discloses a device of the kind having inlet and outlet ducts. In addition to the ducts required for feed and drainage, this design also provides a measurement duct in the instrument by which the bladder pressure is applied to a pressure sensor. The inside bladder pressure measured in this manner controls a pump in the drain line, so that a constant pressure can be maintained inside the bladder.
This design incurs the drawback of substantial additional complexity entailed by the pressure control. This complexity follows from the need to provide a pump in the drain line, and moreover this pump must be a precision pump. Again, the instrument requires a measurement duct in addition to the ducts already present, so that complete redesign is necessary, creating significant problems in finding the necessary space in view of the well-known, exceedingly restricted spatial conditions in which such instruments must be used.
German Offenlegungsschrift 38 05 709 discloses a flushing device similar to the previously mentioned one. In this case an overflow is present in the drain line that keeps the bladder pressure constantly at the static pressure level resulting from the height difference between bladder and overflow. However, the bladder pressure is monitored in the drain line which inherently is always in danger of being clogged. It may be blocked by the tissue pieces released in bladder surgery. Therefore, this design is usable only when using a suprapubic trocar as the drain line and selecting conduits with suitably large cross-sections to prevent any clogging. As regards instruments which must receive both feed and drain lines and therefore can make available only very narrow cross-sections, the use of such designs are precluded. They clearly entail the drawback of additional surgical intervention and difficult handling.
The prior art also includes U.S. Pat. No. 3,900,022, Widran, which has a flushing system. However, Widran includes various control valves and other instruments in the flow path between a pressure regulator and the bladder. As a result, the flow path between the regulator and the bladder includes pressure drops of variable and unknown magnitudes such that the pressure which is registered at the regulator cannot be relied upon as being directly related in any known fashion to the pressure in the bladder.